Hmm, that's not clear to me either, and I know jazz theory really well. I think what they're saying is what degree of the scale, like IV, V, I, and so on. The reason they might say it this way is that there's confusion between numbering scale degrees for chords and for notes. With chords, such as when you outline a chord progression, you name the chords as numbers counting the root as 1. So you might describe a chord progression that goes I - VI - ii - V - I Notice that roman numbers are used to indicate it's chords we're talking about. Notes are also numbered in relation to the root, as notes in a melody or as scale degrees in a chord. In jazz we talk about these using odd numbers only- 1, 3, 5, 7, 9, 11, 13 but inclassical music you may see the even numbers appear there too. Numerals are used to write these numbers. So I think they were using the term 'chordal degree' to indicate that the chord was at (for instance) the sixth degree of the scale from the root, meaning it is a VI chord. But that's an awkward phrase, I'm not sure I'd use it myself.